1. Field of the Invention
The present invention relates to pumps configured to spray washer fluid onto an automotive windshield, headlamp or other surface, to assist a cleaning or wiping operation.
2. Discussion of Related Art
Automotive windshield washer systems now in use in automotive vehicles generally include at least one windshield wiper adapted to be driven by a drive unit to move back and forth across the windshield, a windshield washer pump having an inlet and an outlet, at least one jetting nozzle generally carried on the automobile's hood and fluid-connected with the outlet of the washer pump for spraying a cleaning fluid onto the windshield, and a container or tank for accommodating a quantity of the cleaning or washing fluid and fluid-connected with the inlet of the washer pump.
U.S. Pat. No. 5,184,946 discloses a typical windshield washing system in, for example, that patent's FIG. 1, wherein the windshield washer system comprises a rinsing fluid tank of a generally box-like configuration including four side walls, a bottom wall and a top wall. The top wall of the rinsing fluid tank has a capped supply port defined therein, and one of the side walls has a pump mounting hole defined therein adjacent the bottom wall. A resilient sealing grommet having an annular fitting flange is mounted in the pump mounting hole with the annular flange fluid-tightly welded to the side wall. An automotive washer pump assembly has a generally cylindrical configuration and is pressure-fitted into the tubular grommet so that the pump's inlet is in fluid communication with the fluid contents of the fluid tank. The washer pump assembly is used to supply the washing fluid within the tank by pumping the fluid to at least one spray nozzle through a tubing to spray the washing fluid onto a windshield thereby to assist a wiping operation performed by a windshield wiper. As is well known, the jetting nozzle is generally disposed on a bonnet or hood in an automotive body structure and is aimed at the windshield. Other patents on similar systems in this field include U.S. Pat. Nos. 5,181,838 and 6,053,708, and all three of these patents are incorporated herein, for purposes of nomenclature and to illustrate the background of the automotive windshield washing art.
The automotive washer pumps used are typically of a centrifugal type wherein the fluid medium is supplied by the action of a centrifugal force. A centrifugal pump is a roto-dynamic pump that uses a rotating impeller to increase the pressure of a fluid. Centrifugal pumps are commonly used to move liquids through a tubing or piping system. The fluid enters the pump impeller along or near to the rotating axis and is accelerated by the impeller, flowing radially outward into a diffuser or volute chamber (or casing), from where it exits into the downstream piping system. Centrifugal pumps are typically used for large discharge through smaller heads. An impeller is a rotating component of a centrifugal pump, usually made of plastic, steel, bronze, brass or aluminum, which transfers energy from the motor that drives the pump to the fluid being pumped by accelerating the fluid outwards from the center of rotation. The velocity achieved by the impeller develops increased fluid pressure within the pump's volute when the outward movement of the fluid is confined by the pump casing. Put another way, the impeller's purpose is to convert energy of an electric motor into velocity or kinetic energy and then into pressure of a fluid that is being pumped. The energy changes occur into two main parts of the pump, the impeller and the volute. The impeller is the rotating part that converts driver energy into the kinetic energy. The volute is the stationary part that converts the kinetic energy into pressure. Impellers are often configured as short cylinders with an open inlet (called an eye) to accept incoming fluid, vanes to push the fluid radially, and a splined, keyed or threaded bore to accept a driveshaft. Typical automotive washer pump assemblies use plastic impellers and cylindrical volute casings and so are economical to manufacture, but are limited in that they have problems working with colder fluid, which can be significantly more viscous that typical washing fluid at normal room temperatures.
Variations in fluid pressure can have an adverse effect on windshield cleaning, especially in some modern systems, which typically employ fluidic circuits in the nozzle assemblies used to aim spray at the windshield or headlamp. Modern systems sometimes require high operating pressures and flow rates; for example, when the automobile is in motion, the passing air tends to depress the spray, thus it is necessary to have high nozzle operating pressures if the cleaning fluid is to be sprayed in a satisfactory pattern. Similarly, efficacy of headlamp cleaning depends on the nozzle pressure, thus calling for a pump with a higher performance Pressure-flow rate (P-Q) characteristic. In cold weather, as noted above, the washer fluid viscosity increases and pump pressures are typically reduced. As a result, the nozzles operate at lower pressure in cold weather, leading to reduced windshield cleaning performance in cold weather. The performance of a washer pump in cold weather is referred to as “cold performance” and it is very desirable to improve this aspect of a washer pump's operation, i.e. a better pump P-Q curve at higher viscosities. Washer fluids or liquids used at such temperatures include alcohol mixtures with water having low freezing points. Thus, the viscosity of the liquid is high (e.g. 25 centipoise (“cP”), where water viscosity at Room Temperature (“RT”) is ˜1 cP).
The prior art washer pumps included are not satisfactory for many applications, such as windshield or headlamp cleaning with a mixture of 50-50 ethanol-water at −4F, and those washer pumps typically provide only marginally satisfactory Pressure-Flow Rate (P-Q) performance.
It is with these and other considerations being kept in mind that the designs of the embodiments of the present invention were created.